In 1981 EMD released its next road-switcher to succeed the highly successful SD40-2 (which was still in production at the time), the SD50. This locomotive carried the builder's latest prime mover the 16-cylinder, model 645F3B. For the first time since Electro-Motive cataloged diesels, beginning with the FT of 1939, reliability became a problem in the SD50. Despite its power and new microprocessor controls the model's latest 645F engine, which had been so reliable on the SD40-2 and other earlier designs, was riddled with mechanical trouble and the electrical system was difficult to maintain. When EMD pulled the plug on the SD50 in 1985 just 361 units had been manufactured, less than 10% of the sales of the SD40-2. General Motors' subsidiary knew it needed a new power plant, and quickly, to not only repair its reputation but also keep pace with General Electric.
After going back to the drawing board EMD released the SD60 in 1984, which carried the new model 710 prime mover. This diesel engine corrected the flaws of the 645F while offering more power by further increasing displacement to 710 cubic inches. However, the power plant still carried a two-stroke, "V" design that has always been uncommon in the world of diesel locomotives. Its engine speed of 900-950 rpm stayed true to the 645 model although horsepower took a jump to 3,800 over the 3,600 normally offered among EMD's standard line up until that time. The 710 did usher in two new features from all earlier Electro-Motive prime movers; it was offered only with turbocharging and had electronically-controlled unit injectors (the previous 645 and earlier 567 used mechanically-controlled unit injectors).
The improvements to the SD60 paid off as railroads returned to EMD in larger numbers albeit the manufacturer would not recover its status as top locomotive builder, which was lost to GE following the SD50 debacle. There were several variants of the original including the SD60I (featuring the "Whisper Cab" or Isolated Cab), SD60F (ordered only by Canadian National with a cowl carbody), SD60M (sporting a wide-nose cab), and the SD60MAC (a wide nose cab with AC traction). Among them all Electro-Motive sold more than 1,000 examples before production ended in 1995. Buyers included Conrail, CN, Union Pacific, CSX, Chicago & North Western, Burlington Northern, Kansas City Southern, and Soo Line. The '60 line was also the last to be cataloged as a four-axle Geep. Built from 1985 through 1992 it sold surprisingly well with more than 300 outshopped.
Following this was EMD's SD70 line. It was first introduced in 1992/3 as simply the SD70 featuring 4,000 horsepower using the 710G3B prime mover. The original model sold just a few hundred examples but its many variants during the last 20+ years have been far more successful. One reason for this is, of course, the much improved 710G prime mover. However, new EMD products like the HTCR truck (high-traction, six-axle, radial) that steers itself through curves has also been insturmental in keeping customers returning to the builder. Among Electro-Motive's more successful models from the mid-1990s through 2003 included the SD70M that sold more than 1,500 units and the SD70MAC that saw over 1,000 sales. These designs offered between 4,000 and 4,300 horsepower, which has become the accepted industry standard in recent times.
During the mid-2000s Electro-Motive released the SD70ACe to meet EPA "Tier II" mandates on diesel emissions. To do so the builder employed its 16-710G3C-T2 engine, capable of producing 4,300 horsepower (its DC version is the SD70M-2). The 'ACe remained a respectable competitor to General Electric's Evolution Series for many years in the domestic, U.S. marketplace. However, by 2015, new Electro-Motive owner Caterpillar/Progressive Rail was not able to make its 710 prime mover compliant with the new EPA Tier IV standards that went into effect that year. As a result the SD70ACe, EMD's primary road-switcher model, was shelved. In it place, Progressive Rail released the SD70ACe-T4, which debuted in October of 2015. The manufacturer hopes this new, emissions-compliant model will provide GE with significant competition in the coming years.
For more reading on Electro-Motive locomotives over the yeras and consider the book EMD Locomotives from author Brian Solomon. The book highlights the history of EMD from its earliest beginnings in the 1920s, to its phenomenal successes in the mid-20th century, and finally its decline into second spot behind General Electric in the late 20th century and eventual sale by General Motors in 2005. The book features 176 pages of EMD history and is filled with excellent photography and illustrations. If you might be interested in purchasing this title please visit the link below which will take you to ordering information through Amazon.com.